In recent years, there have been reported many examples in which a photonic crystal is applied to a semiconductor laser. Japanese Patent Application Laid-Open No. 2000-332351 (Patent Document 1) describes a surface emitting laser in which an active layer containing a luminescence material is provided and a two-dimensional photonic crystal is formed in the vicinity of the active layer. This is a type of distributed-feedback (DFB) laser. In this two-dimensional photonic crystal, columnar holes are periodically provided in a semiconductor layer and the refractive index distribution of the photonic crystal has two-dimensional periodicity. This periodicity causes light produced in the active layer to resonate, thereby forming a standing wave and allowing laser oscillation to take place. This laser-oscillated laser light is extracted in a surface normal direction due to primary diffraction caused by the photonic crystal, and the laser operates as a surface emitting laser.
The above-described two-dimensional photonic crystal surface emitting laser is known to have an annular beam shape in which light intensity is low at the central portion of an emitting region and high in the peripheral portion thereof.
However, a unimodal beam shape in which light intensity is high at the central portion is more desirable in some cases for the case of, for example, coupling with a single-mode optical fiber. In order to obtain such a unimodal beam shape, Japanese Patent Application Laid-Open No. 2004-296538 (Patent Document 2) discusses a surface emitting laser light source in which the symmetry of the lattice structure of a two-dimensional photonic crystal is broken by shaping each hole of the two-dimensional photonic crystal into, for example, an equilateral triangle, thereby obtaining a beam shape close to a unimodal beam shape.